Note 12 - Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]

	Balance at December 31, 2015		Balance at December 31, 2014		Input Hierarchy Level
Assets:
Cash and cash equivalents:
Money market funds and other bank deposits	$	155,209	$	209,665	Level 1
Non-current investments:
Equity securities – mining industry		1,515		4,920	Level 1
Trade accounts receivable:
Receivables from provisional concentrate sales		13,490		17,696	Level 2
Derivative contracts:
Base metal forward contracts		—		11,347	Level 2
Restricted cash balances:
Certificates of deposit and other bank deposits		999		883	Level 1
Total assets	$	171,213	$	244,511
Liabilities
Derivative contracts:
Base metal forward contracts	$	283	$	—	Level 2